NAMS 2002 Workshop - ICOM 2008

Asymmetric Polymeric Membrane Formation – 4
Tuesday July 15, 10:30 AM-11:00 AM, Wai’anae
The Impact of Solvent on the Microstructure of Integrally Skinned
Polyimide Nanofiltration Membranes before and after casting
D. Patterson (Speaker), Department of Chemical and Materials Engineering, The University of
Auckland, Auckland, New Zealand, darrell.patterson@auckland.ac.nz
S. Costello, Department of Chemical and Materials Engineering, The University of Auckland,
Auckland, New, Zealand
A. Havill, Department of Chemical and Materials Engineering, The University of Auckland,
Auckland, New, Zealand
Y. See-Toh, Department of Chemical Engineering and Chemical Technology, Imperial College,
London, UK
A. Livingston, Department of Chemical Engineering and Chemical Technology, Imperial College,
London, UK
A. Turner, School of Biological Sciences, The University of Auckland, Auckland, New Zealand
Due to their excellent resistance to a range of solvents, integrally skinned
polyimide membranes have been used as nanofiltration membranes to achieve
selective separations in a range of industrial and lab-scale chemical operations.
These include: homogeneous catalyst recycle, petrochemical dewaxing, solvent
exchange and chiral resolutions. However, despite the widening scope of use of
these membranes, there is still little understanding of how different casting and
filtration solvents affect their microstructure and how this impacts on membrane
separation performance. Part of this question arises because the microstructure
of nanofiltration membranes are typically characterised using dry membranes.
However, during a filtration, the structure of the membrane changes when in
contact with the solvent to be used, especially due to swelling. Therefore,
although imaging a membrane outside of a solvent (dry) may give an indication
of the initial microstructure prior to filtration, in order to understand how the
microstructure affects the transport mechanism and thus membrane separation
performance when it is being used, the membrane must be imaged when in
solvent (wet).
As a first step towards answering the above question, integrally skinned
nanofiltration membranes were fabricated by phase inversion using Lenzing P84
polyimide. A range of P84 membranes were fabricated, varying three formation
parameters: doping solution solvents, evaporation time and post heat treatment
temperature. The doping solvents used were n-methyl-2-pyrrolidone, dimethyl
sulfoxide, dimethylformamide, 1,4-dioxane and acetone. The evaporation times
varied were 10 seconds, 30 seconds and 60 seconds. The heat treatment
temperatures were 100°C, 150°C and 200°C. The effect these parameters had
on the membrane microstructure, filtration performance and mechanical strength
were then characterised. The microstructure of these membranes, dry and in